Adhesive cement solution containing a sulfur-cured rubber



Patented Sept. 9, 1952 ADHESIVE CEMENT SOLUTION CONTAINING ASULFUR-CURED RUBBER Harry J. Hoffman, Detroit, Mich., assignor toMinnesota Mining & Manufacturing Company, St. Paul, Minn., a corporationof Delaware No Drawing. Application February 20, 1948, Serial No. 9,949

7 Claims.

This is a continuation-in-part of my prior co- Dending applicationSerial No. 567,323, filed December 8, 1944, now abandoned.

This invention relates to adhesive cement compositions having a rubberybase. More particularly it concerns adhesive cement compositions havingimproved properties as a result of having the rubber content of thecement sulfur-cured as hereinafter described more in detail.

Heretofore rubber cements have been made of ordinary natural rubber (inunvulcanized form), 1. e. crude rubber, and of such depolymerized rubberas ordinary reclaimed rubber. Natural rubber has been used for decadesin the making of adhesives for surgeons tape and electrical tape, asshoe cements, and such like. Reclaimed rubber cements are illustrated bythe disclosures of the Zimmerli et a1. Patents Nos. 1,937,861 and1,892,123. It has also been suggested heretofore to make adhesivecements of one type or another from various synthetic rubbers.

The utility of such prior cements was limited in respect to a number ofuses by (among other things) the amount of plastic flow of the finaldried film of such cements. This limitation of utility has been morepronounced in respect to cements made with certain rubbers than it hasbeen with others. For example, it has been more pronounced in the caseof such a synthetic rubber as Buna-S synthetic rubber than in the caseof reclaimed rubber, such as used by Zimmerli et al. The reclaimedrubber adhesive cements, as heretofore made, have still otherlimitations on their utility, however.

My invention involves accomplishing, by the method hereinafterdescribed, what has heretofore never been done, insofar as I am aware.That is, I secure improved results by producing an adhesive cement inwhich the rubber component has been sulfur-cured as hereinafterdescribed.

It has heretofore been understood, and correctly so, that ordinaryvulcanized rubbers, such as ordinary inner tubes or tires of commerce,will not dissolve in gasoline. They may swell somea what when exposed togasoline for a long period of time, but they will not either disslove ordisperse in a hydrocarbon liquid such as ordinary gasoline. Ordinarycrude natural rubber, on the other hand, is readily soluble in aliphatichydrocarbon solvents such as ordinary gasoline.

Reclaimed rubber, for use in making adhesive cements, is likewisereadily dispersible in ordinary aliphatic hydrocarbons such as ordinarygasoline, as illustrated by the aforesaid Zimmerli et a1.

patents. Reclaimed rubber, prepared by high temperature digestion,refining and plasticizing of vulcanized rubber, is actuallydepolymerized rubber and is not the same as either crude rubber orsulfur-cured rubber, as is well understood by those skilled in the artand as can be demonstrated by analytical methods such as infra-redspectroscopy. Such depolymerized rubber is more closely equivalent tocrude rubber than to sulfurcured rubber, as evidenced by its action onthe rubber mill as well as its ready dispersibility in gasoline andother aliphatic hydrocarbons.

But vulcanized inner tubes, rubber footwear and other manufacturedrubber articles of the type best known to everyone (which excludesordinary unvulcanized natural rubber such as latex crepe or smokedsheets) are not soluble or dispersible in such solvents. Neither arethey soluble or dispersible in any kind of hydrocarbon solvents, eitheraromatic or aliphatic.

I have found, however, that I can make solventtype adhesive cements inwhich the rubber component has been sulfur-cured, by following theprocedure of blending the rubber component in raw or depolymerized statewith a suitable tackifying resin, and blending therewith a suitable theabsence of effecting the sulfur-cure in the presence of the resincomponent as herein defined, such cure would make the rubber componentnondispersible in an aliphatic hydrocarbon ordinary gasoline.

By non-dispersible I mean that such a sulfur cured product, produced inthe absence of the resin, would be mainly undissolved by such a solvent,even though, if ground up, it might contain a minor percentage ofmaterial which might be extracted by such a solvent, leaving theremainder undissolved and undispersed, i. e., in the form ofswollenlumps or particles, unsuitable for application by brushing orspraying.

Tospecifically illustrate one embodiment of my invention which welldemonstrates some of its important advantages, I will now describe inde-' such as tall one of my adhesive cement compositions and mypreferred method of producing the same.

Ethyl alcohol 35 Volatile hydrocarbon solvent (petrobenzol,

a petroleum solvent having a boilingpoint range of 140-210" F. andweighing 5.83 lbs. per gallon) 24.60

suitable rubbery butadiene-styrene copolymer is a copolymer of '72 partsby weight of butadieneand 28 parts by weight of styrene, copolymerizedby the emulsion process with the use of .a fatty acid soap. (In commercesuch polymer is known as GRS-50.)

The, diolefin resin has a melting point, by the balliand ring method, of230-245 F., and a specific gravity at 60 F, of 1.090-1.120. It is aresinous material of hydrocarbon origin, and usually of a reddish browncolor and a translucent nature, produced by the polymerization ofolefins obtained in the cracking of petroleum.

Thearomatic resin has a specific gravity of,

1.00, a boiling range at 1 mm. of 360-537 F., and a viscosity at 100? F.of 938 centistokes. It is a highly aromatic hydrocarbon product derived.

from petroleum. Atordinary room temperatures it is a soft, semi-fluid,plastic material, usually ofa light brown color and translucent nature.

The pure hydrocarbon thermoplastic terpene resin employed in Formula 1has a zero acid numher and a melting point of C.

The BunaS polymer is firstwarmed. up on a.

rubber mill, and the dipentamethylene thiuram tetrasulfide (which is thesulfur-curing agent in the-formula), thezincoxide pigment, and 200 lbs.;of the diolefin resin are separately added and uniformly milled into thepolymer. base is then removed from the mill in sheets, and placed. in anautoclave whereit is heated for 3 hoursunder 30 lbs/sq. in. gauge, steampressure (274" F.) for curing.

The cured. stock is-then returned to'thei'nill,v

where it is worked for about 5 minutes, after which the remaining 150lbs. of diolefin resinis added and the batch milled until uniform. Itisthen removed to a steam-jacketed heavy duty internal mixer, such as ,aBaker-Perkins mixer, heated by steam at 40 lbs/sq. in. in the jacket.Thearomatic resin and the terpene resin. are then carefully added. Thewell-mixed batch is then cooled, by running cooling water through thejacket of the mixer, and 200 gallons of the petrobenzol is slowly addedto produce a thick,

heavy: plastic mass. The batch is usually cooled to about 200 F. beforethe petrobenzol is added.

The zinc resinate, a light-colored reaction product of zinc oxide andwood rosin, is separately dissolved in 300 lbs. of the petrobenzol andthe 35 lbs. of ethyl alcohol. This solution is then added to the plasticmass'in the internal mixer, and the balance of the petrobenzol is thenadded to provide the desired viscosity.

The milled The resulting product is ready for use as an adhesive cement.One of its illustrative uses is in the bonding of trim cloth toasphalt-impregnated fiber-board in the fabrication of automobileupholstery and trim. In this operation, the areas of both cloth andboard adjacent the edges are coated with the adhesive by applicationfrom a spray gun. The cloth is stretched tightly across the'face of theboard, and the coated edgesof thecloth bonded to the coated edges of therear surface of the board by pressing the partially driedadhesive-coated surfaces together. Immediately the assembly may beexposed totemperatures of 160 to 180 F. without drying oven.

disrupting-the bond or loosening the cloth, as by passage of thecloth-trimmed panels through a If instead of using the adhesive cementof Formula 1, a Buna S synthetic rubber cementnot having my sulfur curewere employed in the use just mentioned, the trim cloth, with itsinherent .tendency to spring; away from the fiber-board, would springaway from the same during passage of thepanelthrough the oven andthebond would be disrupted.

The cement of Formula 1 has many other uses, but the foregoing isillustrative of some of its .advantageous properties. In addition, thedried film has high internal strength, both at ordinary roomtemperatures, as Well as at higher and lower 1 temperatures.

In making up the cement of'Formula 1,,the

dipentamethylene. thiuram tetrasulfide is the. sulfur-curing agent. andserves to cure the S rubber so that theadhesive cement composition, whenapplied as a coating or film in'usage, has high resistance toplasticflow even before. all of the solvent has evaporated.

If the amountofzBuna S rubber-shownin Formula 1 were heated for the timeandtemper: ature mentioned above, namely, 3 hours at atemperature of 274F., .with'the sulfur-curing agent.

named, but inthe .absence of the resin .asprovided for, the resultingsulfur cured product,

would'not be soluble or dispersible in a volatile hydrocarbon solvent.such as the. petrobenzol mentioned. 'If an attempt were made to dissolveor disperse BunaS synthetic rubber cured with a sulfur curing agentasillustrated (the curing,

being efiected in the absence of admixed resin or tackifier), in asolvent such as petrobenzol,

even if such a sulfur cured product were cut up into rather smallpieces, it would be found that such pieces of such sulfur curedrubberwould remain largely undissolved even: after a long period oftime, and even following much mixing, thus making it impossibleto'usesuchmaterial in the practical production of adhesive cements.

Another example of a composition. involving thesame principle as that ofFormula: 1,. but where the composition. has a' higher. viscosity.desirable in certain uses, is as follows:

Olefin resin (as in Famu1a1 350 Zinc resinate (as in, Formula vl) 1300'Aromatic resin (as in Formula l) 75.

Mineral spirits. 1350' A sulfur-cured mill base. ispreparedfromthepolymer, sulfur-curing. agent; l0'lbs. of the:.zinc oxide, and 200 lbs.of. the olefin resin,.and to; this' cured mill base is added the balanceof the-olefin;

Formula 3 I V v Parts by weight Smoked sheet rubber 100 Antioxidant-(Santovar A, an alkylated polyhydroxy phenol) l Sulfur 1 Accelerator(mercaptobenzothiazole) n, 1 Zinc oxide 2 Diolefin resin (as inFormula 1) Limed rosin (wood rosin treated with 7% hydrated lime)--- 10HPetrobenzol 400 The rubber, antioxidant, sulfur and accelerator, zincoxide, and diolefin resin are milled together on the rubber mill. Themill batch, in sheetform, is then heated for 3 hours at lbs. steampressure to provide sulfur-curing of the rubber. The cured base isre-milled, and 30 parts of the limed rosin is added and milled in untilthe batch is smooth. Itis removed in sheet form, out into small squares,and, together with the remaining 70 parts of limed rosin, is dissolved(dispersed) in the petrobenzol solvent by means of a paddle type mixer.

Inthe rubber goods industry rubber is ordinarily cured with 1% of sulfurand suitable accelerators -to provide solvent-resistant rubber goodssuch as insulation, hospital sheeting, rubber mountings and the like,which are insoluble and cannot be dispersed in solvents such aspetrobenzol. However, the above formula (which employs 1% of sulfur),due to the practice of the present invention,'provides an adhesivecement composition in which thesulfur-cured rubber is efiectivelydissolved or dispersed in petrobenzol. The product is 'sprayable withoutcobwebbing and blotching; dried coatings thereof are smooth, and arehighly resistant to plastic flow, and also have high internal strengths.7

Formula 4 U i Pounds Rubbery copolymer of 65 parts butadiene,

parts acrylonitrile (a Buna N rubber) 100 Zinc oxide 5 Antioxidant(Santovar A) .f 1 Pentamethylene thiuram tetrasulfide 1.5 Tributylphosphate (plasticizer for Buna N) 20 Glycerine esterofgasoline-insoluble fraction of pine wood extract (Vinsol Ester Gum) '75Dixie clay 7.5

Resinous heat-reactive oil-soluble product of para-tertiary-butyl phenoland formaldehyde (Beckacite 1003) 30y Aromatic resin (as in Formula 1)20 Terpene resin (as in Formula 1) 15 Methyl isobutyl ketone (volatilesolvent) 600 The procedure. employed in preparing a sprayable adhesivecement composition having .the above formula is similar to thatdescribed in connection; with Formula 1. The polymer, zinc oxide,accelerator. sulfur-curing agent, P135151:

cizer; and 30 lbs. of the resinous ester are first milled together,thencured by heating for 43 hours at about 274 F. (30 lbs/sq. in.steam). Afurther l5 lbs. of the ester is milled into the cured batch,and the clay is also milled in. The batch is then transferred to theinternal mixer, where the balance of the resinous ester, the otherresinous components, and finally the solvent are added and well mixedin. The mixer is heated with jacket steam at lbs. per sq. in. pressureduring the addition of the resins, the temperature of the rubbery massremaining much lower than that of the jacket steam. The mass then iscooled before the solvent is added.

Buna N type polymers are not soluble in gasoline but are readily solublein volatile organic solvents such as methyl ethyl ketone, methylisobutyl ketone, etc. to produce viscous solutions which cobweb badlywhen atomized with air. When heated with sulfur-curing agents in theconventional way, Buna N is rendered insoluble and non-dispersible insuch solvents. However, sulfur-curing the polymer in accordance with thepresent invention, e. g. by. the above-described procedure, provides asmooth, stable, sprayabl-e adhesive cement composition which also hasgreatly improved resistance to plastic flow in the form ofa dried filmand much increased internal strength.

Formula 5 Another specific composition embodying the principles of thepresent invention is a sprayable heat-insulation composition.Sprayability provides for the application of the material in desirablythick and close-fitting coatings to curved and otherwiseinaccessible-structural members, such as automotive floors anddashboards, aircraft heater ducts, etc., Where pre-formed batts orsheets of cellular insulating material are difficult or impossible toapply.

The reclaimed rubber, which contains about 62% of rubber hydrocarbon,issoftened by milling on a rubber mill, and the zinc oxide is milled in.The mixture is then transferred to a heavy duty internal mixer (of theBaker-Perkins type) and half of the limed rosin is added in smallportions and mixed into the batch. The dipentamethylene thiuramtetrasulfide is then added and mixed in, after which the mixer is heated(as by 40 lb./sq. in. jacket steam) to obtain a. tempera.- ture of 250F. in the rubbery mass, which. temperature is maintained for 1 /2 hours.During this time the rubber is sulfur-cured and the mixture becomes dryand crumbly. The remainder of the limed rosin, together with theantioxidant, is then added, and mixing continued until the mass knitstogether and becomes. smooth and homogeneous;

The mixture is now cooled to about 200 F., by passing cooling waterthrough thejacket of the mixer. About 10% of the solvent is addedslowly, so asto guardagainst breaking. of the mass;

of a conjugate-diolefin hydrocarbon (either alone or with one or moreadditional 'polymerizable monomers). Crude rubber is classifiable as apolymer of a conjugate-diolefin hydrocarbon alone, i. c. it is a polymerof isoprenaand reclaimed rubber is a depolymerized form of vulcanizedcrude rubber. Buna Sand Buna N are each copolymers of a major proportionof a conjugate-diolefin hydrocarbon, viz. butadiene, with anotherunsaturated monomer: which is styrene or the like in the case of Buna Stypes of rubber and acrylonitrile or the like in the case of Buna Ntypes of rubber. Examples of unsaturated monomers in addition to styreneand acrylonitrile, are isobutylene, methacrylonitrile, methyl styrene,2-vinyl pyridine, and the like. Butyl rubber is an example of acopolymer of a minor proportion of a conjugate diolefin hydrocarbon,viz. butadiene or isoprene, with av major proportion of isobutylene.

Polymers of conjugate-diolefin hydrocarbons, as above described andillustrated, lend themselves to sulfur-curing.

It will be noted that in Formula 1 the weight of the resinous componentsamounts to substantially 1 times the weight of the rubber, i. e. 151.1parts of resins to 100 parts of the rubber. Formula 2 likewise hassubstantially 1 times as much resin as rubber, i. e. 145 parts of resinsto 100 parts of rubber. Formula 3 has a resin to rubber ratio of120:100, and Formula 4 a ratio of 1401100. The resin-to-rubber ratio ofFormula 5 is 100:100. Thus the preferred resin-to-rubber ratio, asillustrated herein, is Within the approximate range of 1:1 to 15:1.

In this specification and in the appended claims I employ the termssulfur-cure, sulfur-cured and the like, in respect to the treatmentgiven to the rubbery polymers employed by me in making my adhesivecements, herein described. The sulfur-cure may be effected with any of anumber of sulfur-bearing materials ordinarily used in rubber compoundingas rubber vulcanizing agents. Hereinabove I have mentioneddipentamethylene thiuram tetrasulfide. Other analogous sulfurcuringagents are tetramethyl thiuram disulfide, tetraethyl thiuram disulflde,and selenium diethyl dithiocarbamate. It will be noted that thelast-mentioned material contains selenium instead of sulfur, but it isso analogous to the sulfur-bearing materials that I am including itherein under the general designation, sulfur-curing agent. I have alsomentioned herein the use of sulfur as such, plus a suitable accelerator,as illustrated. Other suitable accelerators include benzothiazyldisulfide, and Acrin, a condensation product of hexamethylenetetramine,benzylchloride-mercaptobenzothiazole.

In order to produce an adhesive cement having a sulfur-cured rubberypolymer as herein contemplated, it is necessary for the particularrubbery polymer to be exposed to a time and temperature of reaction withsuch an amount of sulfur-euring agent that, were the rubbery polymerythus treated in the absence of admixed resin as herein called for, itwould be insoluble and non-dispersible in a volatile organic solvent inwhich the uncured rubbery polymer is readily dispersible. Thus it willbe seen that I contemplate a substantial extent of sulfur-curing, asdistinguished from merely a minute amount. Again, in the absence ofadmixed resin, using the amount of sulfur-curing agent and the period oftime and temperatures which I employ, the particular rubbery polymerwould be rendered so unworkable that it could not be practically milledon a rubber mill, as can latex crepe, reclaimed rubber, Buna S and thelike. If an attempt were made to work such product on a rubber mill, itwould break up into shreds,' instead of sheeting out and hangingtogether in the way which latex crepe, reclaimed rubber, and the likewill do when subjected to milling.

Hereinabove I have described important unique and original features andaspects of my inven tion, and have set forth in detail several specificembodiment thereof. It will be understood that this is by way ofillustration and not by way of limitation. My invention makes availableimportant new results in the adhesive cement art, both in terms of thecharacteristics of the finished adhesive cemens and also in terms of theusefulness and usability in adhesive cement manufacture of Buna S, BunaN and various other rubbers. All embodiments within the scope hereof andof the copended claims are comprehended.

What I claim is: 1. Method of making a stable, sprayable vis cous liquidadhesive cement composition comprising (1) blending together 100 partsby Weight of a vulcanizable gasoline-soluble conjugate-diolefinhydrocarbon rubbery polymer, 15-120 parts of a hydrocrabon-solubletackifier resin compatible with said polymer, and an excess of asulfurcuring agent over the amount normally required for sulfur-curingof said rubbery polymer, in'the absence of said resin, to insolubilityin gasoline, (2) heating the blend for a time and at a temperaturesufficient, in the absence of said resin, to cause sulfur-curing of saidrubbery polymer to insolubility in gasoline, and (3) dispersing'theheated blend, together with additional hydrocar- Icon-soluble andpolymer-compatible resin, ina volatile hydrocarbon solvent, the'amountof said resin added to the blend subsequent to the sulfur-curing stepbeing at least approximately as great as that added prior to saidsulfur-curing step. I

2. In the manufacture of a stably viscous, sprayable liquid adhesivecement composition characterized in that upon application as abondingfilm'or adhesive coating it at first becomes highly tacky and uponfurther evaporation of solvent it dries to a substantially non-tackystate and provides a film or bond of a tough, elastic, rubbery naturewhich maintains high bonding strength at elevated temperatures of theorder of l60-180 F., the method comprising; (1) blending together partsby weight of a vulcanizable gasoline-soluble conjugate-diolefinhydrocarbon rubbery polymer, about 20-40 parts of hydrocarbon-solubletackifier resin compatible with said polymer, and an excess of sulfurcuring agent over the amount normally required for sulfur-curing of saidrubbery polymer, in the absence of said resin, to insolubility ingasoline, (2) heating the blend for a time and at a temperaturesufficient, in the absence of said resin, to cause sulfur-curing of saidrubbery polymer to insolubility in gasoline, and (3) dispersing theheated blend, together with additional hydrocarbonsoluble andpolymer-compatible resin to a total amount of not more than about 300parts, in a volatile hydrocarbon solvent, the amount of said resin addedto the blend subsequent to the sulfurcuring step being at leastapproximately as great as that added prior to said sulfur-curing step.

3. In the manufacture of a stably viscous, sprayable liquid adhesivecement composition rubbery-nature which-- maintains: high bondingstrength-at elevatedtemperatures of the order'of 160 180 11," the methodcomprisingzr (1)1 blending tdgeth'er 100 partshy weight of a vulcaniza-'ble gasol-ine-soluble conjugate 'diolefin hydrocarbon-rubbery "polymerconsisting .mainly of butadie'ne styrene syi'itl ietio--rubber, about'40 parts of hydrocarbon-soluble -tackifier resin compatible with-isaidpolymer, and an excess of sulfurcuring agent over: the amount normallyrequired, .in'the absence :of saidfresin; for sulfurecuring :of saidrubbery polymer to :insolubility in gasoline; (2) heatingfthe blend fori a time: and at: a temperature .sufil'oicnt, in'rthe absence of "saidresin; to cause isul fur curing ofi-said rubbery-polymer to:insolumentcomposition, istably :uniiormiunder. normalconditiohspfistorage, and: shipping, produced in accordance withclaim 2,:saidcomposition-v being further.- zcharacterized ,rin that, .7 upon 1application tma rsu iaiiei aszanthin coatingand evaporationof solvent,it passes through a highly tacky state andzdriesrtol-sa ztacki-free:state, the-dried film beingtrtouglrurubbery :andnelastic, andmaintaining alzhighrbonding: strength :and. internalstrength at elevatedtemperatures'of the: order of 160 -180 F.

.6.w; Azivisoous liquid (solvent-type adhesive cecQmpQsition, .;stab1-yuniform 'under normal conditions :of storage and shipping; produced inaccordance: with A 01353113, said composition being made from ;a rubberypolymer composed mainly ofa rubbery-butadiene-styrenecopolymensulfurcured -:in :the. :presence iof a min'orproportion :ofthetotarresin :contentsofzthe composition; saidcompositionzbeingiurthercharacterized-imthat,

upon :application .to; a :surfaceasia thinxcoating andzevaporation; of;'solyent;:it: passes .throughia highlytacky statezand'driestota;tack-.free.zstate, the dried ifilm:. being ,to .ugh;rubbery andelastic, and maintaining :a high.;bonding. "strength :andinternalv'strength at. elevated temperatures: ofgth'e order: of;16l1-.-I F;

7; In :the'; manufacture 10f rai=stablyiviscous, sprayable: e liquid i'.adhesive cement. zcomposition characterized .in'that uponapplicationaas:a bond.- ing gfilmi: or '"adhesivex-coating it: at first become highly'taokyxandluponffurtherrevaporation ofthe solvientrit. dries to. asubstantially non tacky. state and provides-a .'or;:bond ofaztonghgelastio, rubbery nature-which 1maintains thigh-mending strength:at elevatedtemper-atures; of the orderof -180 F., a method comprising:(l );.,blending togetherxrlOOipartsfcby weighttof a vulcanizablegasolinee'solubl'e conjugate-adiolefin hydrocarbon rubbery polymer, atleastiabout;lfli'partszof 'hydrocarbon-solublertackifieriresin:compatible with said c-zpolymen': and;an excess: :of. sulfur-curing agentxover; the amount. normally *requiredfor sulfur-touring of; said zrubberyipolymer in'the ab sence ofIsaidresin-toinsolubility in gasoline, (2') heating i the 'blend for. :atime. and at: a tempera. ture' isufiicient; in the absence :of saidresin, to cause. sulfuracurin of said 1 rubbery polymer to insol'ubilityinz'gasoliney and :(3 )1 dispersing the heatedblend, together-withadditional. hydrocar bon-soluble'mand pol-ymeracompatible "resin :to :atotal amount of atleastaboutilZOparts,:in a volatiiehydrocarbonsolventrHARRY J..'HOFEM-AN.

,RZEFERENGES CITED Thefollowingreferenceszare-of record in the file ofthis-patent:

UNITED" STATESPATENTS Number I Name: Date.

1,892,167 Semon-- HDec. 27, 1932 2,080,730 McCortney; May. 18, 1937.2,177,627' 1' Drew 0017.31,. 1939 2,304,071 Bollinger .Decr 8, 1 9422347 211 5 Merrillet al; Apia-25,. 1944 2,352,460 Treves June 27, 1944Kemp Man-4, 2,4i59',891 1 Nelson iet: a1, Jan.- 25,1949

1. METHOD OF MAKING A STABLE, SPRAYABLE VISCOUS LIQUID ADHESIVE CEMENTCOMPOSITION COMPRISING :(1) BLENDING TOGETHER 100 PARTS BY WEIGHT OF AVULCANIZABLE GASOLINE-SOLUBLE CONJUGATE-DIOLEFIN HYDROCARBON RUBBERYPOLYMER, 15-120 PARTS OF A HYDROCARBON-SOLUBLE TACKIFIER RESINCOMPATIBLE WITH SAID POLYMER, AND AN EXCESS OF A SULFURCURING AGENT OVERTHE AMOUNT NORMALLY REQUIRED FOR SULFUR-CURING OF SAID RUBBERY POLYMER,IN THE ABSENCE OF SAID RESIN, TO INSOLUBILITY IN GASOLINE, (2) HEATINGTHE BLEND FOR A TIME AND AT A TEMPERATURE SUFFICIENT, IN THE ABSENCE OFSAID RESIN, TO CAUSE SULFUR-CURING OF SAID RUBBERY POLYMER TOINSOLUBILITY IN GASOLINE, AND (3) DISPERSING THE HEATED BLEND, TOGETHERWITH ADDITIONAL HYDROCARBON-SOLUBLE AND POLYMER-COMPATIBLE RESIN, IN AVOLATILE HYDROCARBON SOLVENT, THE AMOUNT OF SAID RESIN ADDED TO THEBLEND SUBSEQUENT TO THE SULFUR-CURING STEP BEING AT LEAST APPROXIMATELYAS GREAT AS THAT ADDED PRIOR TO SAID SULFUR-CURING STEP.